> Someone realised that if they just don't give feedback for interviews then they can't say something incriminating that could prove they violated labor laws, then everyone started doing it and now it's just the thing that's done.
(Note: I am assuming this is true in the US. This is may not be true in other countries)
Job seeking is inherently a confidential activity for many people, as the interviewee want to make sure that their current job is safe before leaving for a new role. To sue a company because they didn't get the role is to put their current role at risk.
In addition, the company has a lot more power and resources than the interviewee. They can drag the process out to the point where the interviewee withdraws, runs out of money or settle. Given that, the interviewee has to have significant proof as well as resources and privilege to able to successfully sue the company.
All things considering, I don't think the idea of not providing feedback because of legal liabilities is sound.